Semiconductor devices and liquid crystal display devices are produced by the so-called photolithography technique in which a pattern formed on a mask is transferred onto a photosensitive substrate. The exposure apparatus, which is used in the photolithography step, includes a mask stage for supporting the mask and a substrate stage for supporting the substrate. The pattern on the mask is transferred onto the substrate via a projection optical system while successively moving the mask stage and the substrate stage. In recent years, it is demanded to realize the higher resolution of the projection optical system in order to respond to the further advance of the higher integration of the device pattern. As the exposure wavelength to be used is shorter, the resolution of the projection optical system becomes higher. As the numerical aperture of the projection optical system is larger, the resolution of the projection optical system becomes higher. Therefore, the exposure wavelength, which is used for the exposure apparatus, is shortened year by year, and the numerical aperture of the projection optical system is increased as well. The exposure wavelength, which is dominantly used at present, is 248 nm of the KrF excimer laser. However, the exposure wavelength of 193 nm of the ArF excimer laser, which is shorter than the above, is also practically used in some situations. When the exposure is performed, the depth of focus (DOF) is also important in the same manner as the resolution. The resolution R and the depth of focus δ are represented by the following expressions respectively.R=k1·λ/NA  (1)δ=±k2·λ/NA2  (2)
In the expressions, λ represents the exposure wavelength, NA represents the numerical aperture of the projection optical system, and k1 and k2 represent the process coefficients. According to the expressions (1) and (2), the following fact is appreciated. That is, when the exposure wavelength λ is shortened and the numerical aperture NA is increased in order to enhance the resolution R, then the depth of focus δ is narrowed.
If the depth of focus δ is too narrowed, it is difficult to match the substrate surface with respect to the image plane of the projection optical system. It is feared that the focus margin is insufficient during the exposure operation. Accordingly, the liquid immersion method has been suggested, which is disclosed, for example, in International Publication No. 99/49504 as a method for substantially shortening the exposure wavelength and widening the depth of focus. In this liquid immersion method, the space between the lower surface of the projection optical system and the substrate surface is filled with a liquid such as water or any organic solvent to form a liquid immersion area so that the resolution is improved and the depth of focus is magnified about n times by utilizing the fact that the wavelength of the exposure light beam in the liquid is 1/n as compared with that in the air (n represents the refractive index of the liquid, which is about 1.2 to 1.6 in ordinary cases).
As disclosed in International Publication No. 99/49504 as described above, a scanning type exposure apparatus is known, in which the substrate is exposed with a pattern formed on the mask while synchronously moving the mask and the substrate in the scanning direction. In the case of the scanning type exposure apparatus, it is required to realize the high scanning velocity (velocity of scanning) in order to improve, for example, the productivity of device production. However, if the scanning velocity is increased to be high, then it is difficult to maintain the desired state, for example, for the condition (for example, the size) of the liquid immersion area, and the exposure accuracy and the measurement accuracy, which are to be obtained through the liquid, are consequently deteriorated. Therefore, it is required that the liquid immersion area of the liquid is maintained to be in the desired state even when the scanning velocity is increased to be high.
For example, if the liquid immersion area cannot be maintained in the desired state, and any bubble and/or any void (gap) is formed in the liquid, then the exposure light beam, which passes through the liquid, does not arrive at the surface of the substrate satisfactorily due to the bubble and/or the void, and an inconvenience arises, for example, such that any defect appears in the pattern to be formed on the substrate. When the liquid immersion area is locally formed on a part of the substrate while supplying and recovering the liquid, there is such a possibility that it is difficult to sufficiently recover the liquid of the liquid immersion area as the scanning velocity is increased to be high. If the liquid cannot be recovered sufficiently, the adhesion trace (so-called water mark, the adhesion trace of the liquid will be hereinafter referred to as “water mark” as well when the liquid is not water) is formed, for example, due to the vaporization or evaporation of the liquid remaining on the substrate. There is such a possibility that the water mark exerts any influence on the photoresist on the substrate, and there is such a possibility that the performance of the device to be produced is deteriorated by the influence. There is also such a possibility that it is difficult that the liquid immersion area is maintained to have a desired size as the scanning velocity is increased to be high. There is also such a possibility that the liquid of the liquid immersion area outflows as the scanning velocity is increased to be high.